Influence of ignition positions on the flame behavior of non-uniform methane-air mixture explosions in vertically closed pipes

Ignition location determines the propagation mode and the extent of damage of non-uniform gas explosions. The explosion characteristics of non-uniform methane-air mixtures under the influence of three ignition positions (bottom, middle and top) in a vertical closed pipe were investigated. Unstable density stratification was achieved by varying diffusion times, distinguishing it from the homogeneous mixture case. The results demonstrated that if the diffusion time was 1 min, the bottom ignition was more significantly affected by the R-T instability compared to the middle and top ignition, as evidenced by the flame structure. In addition, middle ignition caused a smaller reduction in flame propagation velocity compared to bottom ignition at a diffusion time of 1 min. Furthermore, at a diffusion time of 10 min, top ignition led to the smallest reduction in flame propagation velocity. Overall, ignition location had a greater impact on peak flame velocity than methane non-uniformity.